WEBVTT SPAN ANDTRAFFIC BY EARLY THIS FAL850 DAYS DOWN, ABOUT 177 TO GO,AND PROGRESS ON CONSTRUCTION OFTHE NEW CZAR ROW LON BRIDG.AND TWO BEAMS THAT WILL MAKE UPTHE CENTER LIFT SPAN FLOATED INBY BARGE.>> THEY WEIGH ABOUT416,000 POUNDS A PIECE, AND THESIX PIECES TOGETHER WHEN FULLYASSEMBLED WITH ADDITIONALLIFTING BEAMS AND FASCIA BEAMSWILL WEIGH AROUND4 MILLION POUNDS.REPORTER: THE NEW ACCESS ROAD ISTAKING SHAPE ON THE PORTSMOUTHSIDE.>> THE FIRST TWO OF 15 SPANSHAVE BEEN COMPLETED OVER MARKETSTREET IN NEW HAMPSHIRE.REPORTER: WHAT MAKES THISPROJECT UNIQUE IS THAT IT A LIFTTOWER THAT'S BUILT IN SEGMENTS,LIKE A GIANT LEGO SET AND THATIT SERVES BOTH VEHICLES AND RAILTRAFFIC.THE CENTER STAND WILL GO UP FORSHIPS AND LOWER TO CONNECT TRAINTRACKS BELOW.>> I BELIEVE THAT'S THE ONLY ONEIN NORTH AMERICA THAT OPERATESIN A SIMILAR MANNER.THERE IS A BRIDGE SIMILAR TOTHIS ONE IN BORDEAUX, FRANCE.REPORTER: THE SARAH LONG WASMADE IN NEW HAMPSHIRE AND ISCONSIDERED THE PRIMARY BACKUP TOTHE HIGH 95 BRIDGE.>> THERE'S A LOT OF CHALLENGES,IT'S A VERY COMPLICATEDSTRUCTURE AND THEN WORKING INTHIS MARINE ENVIRONMENT AND THEWEATHER CONDITIONS, WORK, ON THE

The project started in December 2015, with the new bridge being built next to the old one, which carried traffic until it was shut down in August. If all goes as planned, the new bridge will be carrying traffic early this fall.

Three of the four 200-foot towers are done, and the fourth should be completed next week. Two of six 100-foot steel beams that will make up the center lift span have been floated in by barge.

"They weigh about 416,000 pounds apiece, and the six pieces together, when fully assembled with additional lifting beams and fascia beams, it will weigh about 4 million pounds," said project engineer Ron Taylor.

A new access road is taking shape on the Portsmouth side.

"The first two of 15 spans have been completed over Market Street in New Hampshire," Taylor said.

What makes the project unique is that it's a lift tower that's built in segments, like a giant Lego set. It serves vehicles and rail traffic, and the center span will be raised for ships and lowered to connect the train tracks below.

"I believe that's the only one in North America that operates in a similar manner," Taylor said. "There is a bridge similar to this one in Bordeaux, France, but it was not segmentally cast."

The Sarah Long Bridge is one of three bridges connecting Maine and New Hampshire, which are splitting the $158 million cost. It's considered to be the primary backup to the I-95 bridge.

"There are a lot of challenges," Taylor said. "It's a very complicated structure, and then there's working in this marine environment and the weather conditions, working on the river with the tides."

The contract sets an opening date of Sept. 1. Officials with the construction firm Cianbro said the schedule has slipped a bit, but they hope to make it up.

The bridge might also close at times over the winter to make adjustments, and the entire project should be wrapped up by June 2018.